Freezer alarm device



March 29, 1955 D. E. MORAN 2,705,270

FREEZER ALARM DEVICE Filed Dec. 17, 1952 Inventor: Don El. Nor-an,

His AttOV'fleH.

United States Patent FREEZER ALARM DEVICE Don E. Moran, Morrison, Ill., assignor to General Electric Company, a corporation of New York Application December 17, 1952, Serial No. 326,467 9 Claims. (Cl. 200-140 This invention relates to alarm devices for freezers in which perishable goods such as food are preserved and stored in frozen condition for relatively long periods of time.

In the operation of freezers of this type, one of the most important factors is the detection of a rise in temperature before spoilage of the contents occurs. Such a rise in temperature may be due to the failure of the power supply or of the refrigeration unit, the improper closing of a door or lid, or the inadvertent leaving open of a door or lid. Such freezers often contain a relatively large amount of goods, and if spoilage occurs the loss may be serious. For that reason, it is desirable to have an alarm which is entirely reliable at all times.

It is an object of my invention to provide an alarm for freezers which is entirely dependable and adapted to become operative upon an undesired rise in temperature regardless of how long the alarm has remained inactive before the rise occurs. This is desirable because freezers frequently operate for long periods of time without the occurrence of an undesirable rise in temperature.

It is a further object of the invention to provide an alarm device of the character described which is simple and inexpensive to construct.

A specific object is the provision of a thermostatic alarm device of this character in which an electric switch is operated responsively to changes in volume accompanying the solidification and melting of a forced generating material and in which the solidification process takes place always within relatively narrow temperature limits.

Further objects, features, and advantages of my invention will be apparent from the following detailed description of a preferred embodiment thereof, while the scope of the invention is set forth in the appended claims.

In carrying out my invention in one preferred form, I provide a device having a completely closed chamber portion with an expansible wall, with the chamber completely filled with a solution of potassium chromate and water. The potassium chromate and water solution may contain a small amount of a nucleating agent if desired. When this solution freezes, it expands, with a resulting movement of the expansible wall, such movement being utilized through a suitable mechanism to close electric switch contacts. When the surrounding temperature increases sufficiently to melt the potassium chromate solution again, the switch contacts are once more opened, and these contacts may be arranged to open an alarm circuit.

For a clearer and more complete understanding of the invention, reference should be had to the accompanying drawing, in which:

Fig. 1 is a side elevation view in section of a thermostatic alarm device embodying my invention in a preferred form, while Fig. 2 is a sectional view along the line 2-2 of Fig. 1.

In the drawing, a typical alarm device embodying the invention 'is s own: and designated by the numeral 10. The device '10comprises a container 11 which may, for example,"be found in configuration as shown, and which has walls 12 defining a chamber having an upper portion 13 and a smaller depending lower portion 14. hermetically sealed cover 15 may be provided for the container 11 to prevent moisture and corrosion inducing impurities from entering the alarm device. As shown, the cover is sealed on the container 11 by a portion 28 which 2,705,270 Patented Mar. 29, 1955 may be formed conveniently by providing a straight flange portion around the upper margin of container 11 initially and spinning it over during assembly of the device to embrace the outer periphery of cover 15 as shown in the drawing.

The upper portion 13 of the chamber houses a fixed electrical contact member 16 and a movable electrical contact member 17. The latter member, as shown, is serpentine in form having two reverse bends and having a right angle portion at the upper end secured to a conductive terminal member 18 in a suitable manner such as by brazing. Member 17 preferably is of resilient material, and the upper reverse bend, portion 170, of this member and the two substantially horizontal portions 17b and 17d adjacent the upper bend portion may have a" central cut-out portion 29 as seen in Fig. 2, if desired, to provide member 17 with the required spring characteristic. Terminal member 18 extends outwardly through cover 15 through suitable sealing means as at 19 to provide for one external electrical connection to the switch contacts, by means of an insulated conductor 30, for example. The fixed contact portion 16 of the switch similarly extends outwardly through the cover 15, being sealed by a portion 20, thus providing for an electrical connection to the other side of the switch, as by an insulated conductor 31.

A flexible diaphragm member 21, having a depending portion 22 extending downwardly into portion 14 of the chamber, is positioned on the bottom of chamber portion 13. Diaphragm 21 has its margins sealed to the bottom wall of chamber portion 13 in order to provide a seal between chamber portions 13 and 14.

An operating button 23 of insulating material is located between depending portion 22 of the diaphragm and the lower horizontal arm 17e of movable contact member 17. Button 23 has a portion 24 of reduced diameter extending upwardly through a suitable opening in the lower horizontal arm 17e. Suitable upwardly projecting portions 25 and 26 on portion 17e engage portion 24 of the button and cooperate with the shoulder portions 27 formed on the button below portion 24 to retain the button securely in position on movable contact member 17.

Portion 14 of the chamber below diaphragm 21 is completely filled with a solution of potassium chromate (KzCrOt) and water, which solution preferably contains approximately 34%, by weight, of potassium chromate. Such a solution is liquid at ordinary ambient temperatures, but freezes at a temperature of approximately 12 Fahrenheit or below, and when it freezes it expands in volumeapproximately 6.4%. Such expansion causes the depending portion 22 of the diaphragm to push button 23 upward, causing movable contact 17 to engage fixed contact 16. If the temperature is subsequently increased, the potassium chromate solution melts again at approximately 14 Fahrenheit and causes the solution to return to its original smaller volume, which again opens the contacts.

The use of a potassium chromate and water solution as the pressure generating medium in a freezer alarm device has several advantages over other solutions which have been used in similar devices. One of these is that potassium chromate is non-corrosive in a water solution. Another is that the eutectic potassium chromate water solution melts at a desirable alarm temperature for the freezer alarm devices, namely, 14 Fahrenheit. The eutectic solution of potassium chromate and water contains 35.3%, by weight, of potassium chromate, and a solution containing exactly this percentage of potassium chromate may be used if desired. However, I prefer to use a solution containing slightly less potassium chromate, such as 34%, because the characteristics of a potassium chromate and water solution change much less rapidly from the characteristics at the eutectic point as the amount of K2Cr04 becomes less than 35.3% than for an increase in percentage of KzCrOr above 35.3%. Therefore, any variation in the percentage specified, due to manufacturing tolerances and the like, is less likely to affect the operation of the alarm device adversely if the percentage of K2C1'O4 is specified to be slightly below the. eutectic value. Either of these solutions, i. e., 34% potassium chromate or 35.3% potassium chromate, has

a sharp melting point at approximately 14 Fahrenheit regardless of the time that it has been in the crystalline or solid state and therefore provides a very desirable operating medium for a freezer alarm thermostat.

The freezing temperature of the solution is not particularly important, provided that it is not lower than approximately Zero degrees Fahrenheit, inasmuch as most food freezers are operated at approximately Fahrenheit. However, it has been found that in some cases, due to super cooling, that a solution of potassium chromate in water does not freeze until the temperature goes below zero degrees Fahrenheit. To prevent such an occurrence, and provide a substantially uniform freezing temperature above 0 Fahrenheit, nucleating agents may be added to the K2CrO4 solution. These nucleating agents need be added only in very small amounts, and

vvarious material including silver iodide, graphite as aquadag, and certain clays may be used as the nucleating agent. I prefer to use approximately one quarter per cent, by weight, of silver iodide crystals which I have found consistently causes the activating solution. to begin formation of ice crystals at a temperature above 5 F. and thus prevents all but a negligible amount of super cooling.

While I have illustrated and described a preferred embodiment of my invention, modifications thereof may be made by those skilled in the art. Accordingly, it should be understood that I intend to cover by the appended claims all such modifications which fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a thermostatic device, a completely enclosed chamber portion having an expansible wall portion, and a liquid material which increases in volume upon freezing completely filling said chamber portion, said material comprising a mixture of potassium chromate and water.

2. In a thermostatic device, a completely enclosed chamber portion having an expansible wall portion, and a material which increases in volume upon freezing completely filling said chamber portion, said material comprising potassium chromate and water in approximately the proportions of a eutectic mixture.

3. In a thermostatic device, a completely enclosed chamber portion having an expansible wall portion, a liquid material which increases in volume upon freezing completely filling said chamber portion, said material comprising. a mixture of potassium chromate and water, and a small amount of a nucleating material in said liquid material.

4. In a thermostatic device, a completely enclosed chamber portion having an expansible wall portion, a liquid material which increases in volume upon freezing completely filling said chamber portion, said material comprising a mixture of potassium chromate and water, and a small amount of silver iodide crystals in said liquid as a nucleating agent. 5. In a thermostatic device, a completely enclosed chamber portion having an expansible wall portion, and a liquid material which increases in volume upon freezing completely filling said chamber portion, said material comprising a mixture of approximately 34%, by weight, potassium chromate, approximately one quarter per cent, by weight, of silver iodide crystals and the balance water.

' material.

7. In a thermostatic device, a completely enclosed chamber portion having an expansible wall portion, a liquid material which increases in volume upon freezing completely filling said chamber portion, said material comprising potassium chromate and water in approximately the proportions of a eutectic mixture, and a small quantity of silver iodide'crystals in said liquid material.

8. A thermostatic alarm device comprising walls forming a completely enclosed chamber portion, a resilient diaphragm'member forming at least a portion of one of said walls, a liquid material which increases in volume upon freezing comprising a mixture of potassium chromate and water plus a small amount of silver iodide crystals as a nucleating agent completely filling said chamber portion, and contact members arranged for engagement and disengagement upon themovement of said diaphragm responsively to the freezing and melting of said material.

9. A thermostatic alarm device comprising walls forming a completely enclosed chamber portion, a resilient diaphragm member forming at least a portion of one of said walls, a material composed of 34%, by weight, potassium chromate, one quarter per cent, by weight, silver iodide crystals and the balance .water completely filling said chamber portion, additional walls forming a second completely enclosed chamber portion joined to said first chamber portion and having said resilient diaphragm member as a common wall between the said two chamber portions, a movable contact member of resilient material arranged within the second said chamber portion for actuation by the outwardmovement of said diaphragm due to the expansion of said'material upon freezing, a terminal member connected to said movable contact member and extending through one of the walls of the said second chamber portion, and a fixed contact member within the said second chamber portion arranged to be engaged by said movable contact member in response to a predetermined movement of said diaphragm member caused by the freezing of said material, said fixed contact member extending through one of the walls of the said second chamber portion whereby it serves also as a second terminal member, the said material contacting to its initial volume again upon melting which occurs when the temperature of said material reaches approximately 14 F. whereby said contacts are permitted to part upon an increase in the temperature of the said material to this temperature.

References Cited in the file of this patent UNITED STATES PATENTS Raney Oct. 31, 192

OTHER REFERENCES Handbook of Chemistry and Physics, pp. 1240-1241, by Charles D. Hodgman, twentieth edition, published 

7. IN A THERMOSTATIC DEVICE, A COMPLETELY ENCLOSED CHAMBER PORTION HAVING AN EXPANSIBLE WALL PORTION, A LIQUID MATERIAL WHICH INCREASES IN VOLUME UPON FREEZING COMPLETELY FILLING SAID CHAMBER PORTION, SAID MATERIAL COMPRISING POTASSIUM CHROMATE AND WATER IN APPROXIMATELY THE PROPORTIONS OF A EUTECTIC MIXTURE, AND A SMALL QUANITY OF SILVER IODIDE CRYSTALS IN SAID LIQUID MATERIAL. 